In signalling such as in telephone applications, it is desirable to provide each successive ring of the telephone of a greater intensity than the ring which immediately preceeded it. Thus, an initial signal may be of soft intensity while after several rings the intensity may become loud enough to be heard at a considerable distance. U.S. Pat. Nos. 3,387,097 and 3,450,846 relate to the mechanization of this feature utilizing a thermistor, while U.S. Pat. No. 3,343,100 relates to the provision of a sawtooth modulator for producing repeated output crescendos.
The techniques in these aforementioned patents for producing an increasing acoustic signal have been expensive of construction and have generally been relegated to circuits which include tone oscillators within the telephone for driving the telephone acoustic signalling device.